Study on the Three-Dimensional Mechanical Properties of Structural Soft Clay Soils under Unloading Conditions

Soft clay soils are generally structural in nature, and structural properties are an important factor influencing soil deformation characteristics. The soft clay soil of Tianjin Binhai was used as the raw material, and the structural soft clay soil was artificially prepared by mixing a small amount of cement with different contents to produce a nearly homogeneous soil with different structural properties. The test results show that the strain of the soil under lateral unloading conditions is related to the unloading rate, the structure of the soil itself and the consolidation envelope pressure. When the structural properties of the soil and the unloading rate are the same, the smaller the envelope pressure, the faster the strain growth rate of the specimen and the greater the strain during damage. When the structure of the soil is the same as the surrounding pressure, the strain at failure and the stress at failure both increase as the unloading rate increases. When the large principal strain ε₁ is less than the damage strain and the structural properties of the soil sample are not damaged, the slope of the ε₁-ε₃ relationship curve grows at a slower rate, and when the large principal strain ε₁ reaches its peak damage, the expansion rate in the direction of the small principal strain ε₃ accelerates until the sample is damaged. Under the same circumferential pressure, the initial unloading tangential modulus of the soil decreases with increasing unloading rate, and the unloading damage strength of the soil increases with increasing unloading rate. On this basis, the stress-strain relationship was analysed and a prediction formula for the unloading damage strength was established and validated, taking into account the effects of unloading rate and structural strength of the soil sample.